The invention relates to a steam iron comprising a soleplate provided with steam vents for passing steam to a fabric to be ironed and a steam generator for supplying an adjustable amount of steam to the steam vents.
Such a steam iron is known from U.S. Pat. No. 5,042,179. In ironing of clothing three different processes can be distinguished: conditioning of the fibres, relaxation of the fibres and fixation of the fibres. During the conditioning the fibres are prepared for the relaxation. The conditioning is done by increasing the temperature of the fibres in order to make the fibres weak enhancing the recovery, during the relaxation, from the plastic deformation of the fibres caused by wearing of the clothing. The use of steam is an effective way to increase the temperature. Moreover, the weakness of some fibres increases with the water content as well, especially for cotton, linen, viscose and wool. After the conditioning the relaxation or real ironing takes place. During the relaxation the weak fibres are being pressed between the soleplate and the ironing board. This should last sufficiently long to allow the fibres to recover from the plastic deformation. The moisture content of the fabric should not decrease too fast during relaxation in the case of cotton, linen and wool as this would adversely affect the relaxation process. After relaxation the opposite from the conditioning takes place. This means that the weakness of the fibres is decreased to prevent the occurrence of wrinkles again. The fixation comprises the drying of the fibres, followed by cooling down.
During the conditioning the temperature of the fabric increases to about 100.degree. C. partly by condensation of steam and partly due to heating by the soleplate. During the relaxation the temperature should be kept at about 100.degree. C. to maintain both a high temperature and a high moisture content of the fabric providing for a fast recovery of the fibres. After the relaxation the fabric is being dried, indicated by a temperature increase in the fabric above 100 .degree. C., and followed by cooling down to assure a proper fixation. This cooling down takes place partly on the ironing board and partly after removal of the cloth from the board to clear the board for the next cloth.
In conventional steam irons the steam rate is set and the iron is moved forwards and backwards over the fabric. In the forward stroke the amount of steam is insufficient in most cases to heat the fabric up to 100.degree. C., whereas after passing the steam vents the fabric is heated further by the sole plate to a higher temperature close to 100.degree. C. In the backward stroke the production of steam still continues, but the fabric has already reached 100.degree. C. and will not adsorb water any more. Although it does not affect the fabric, steam is wasted that could have been used to warm up and to moisten more intensively the fabric in order to obtain a weaker fabric at a higher temperature during the forward stroke. A lot of unused steam is blown through the fabric into the ironing board and to the surrounding air without the desired condensation onto and in the fabric. A lot of heat and water is wasted and should be avoided.
In the above mentioned known steam iron waste of steam is reduced by controlling the amount of steam produced by the steam generator as a function of time. The steam production is controlled by regulating the output power of the heating element of the steam chamber from a high initial level to a low or zero level during an ironing cycle. It is further known from said known steam iron to adapt the steam production to the amount of heat required to heat the fabric by measuring the power need of the heating element of the soleplate. Such measuring however is inaccurate and slow.